Go one week without using any cash.
Must use charge, debit or EFT. Keep track of the very few times you have to use cash.
I've done this, it wasn't as easy as I thought. Something kept coming up: the charge machine wasn't working or something like that and I don't have a debit card which would take care of some of the smaller stores which only take debit. But the hardest thing was lottery tickets, vending machines and giving money to the homeless (I had decided that I wasn't going to have these count but eventually I had a week go by without having any of the ca$h issues comes up). Since then, I've had a few more cashless weeks but usually I only need a few dollars for little things.